This invention relates to the field of interface hardware for local area networks, and more particularly to a network interface which efficiently switches between different links to a local area network.
Local area networks (LANs) have forever changed corporate and personal computing. First used for sharing simple information and resources among personal computer users, LANs have dramatically evolved over the last ten years to become the premier strategic computing platform for businesses today. All but the smallest corporations rely on LANs and their dependence and appetite for this technology shows no signs for slowing. Indeed, LANs have matured to the point of peer status with personal computers themselves. As the market and deployment of ever more powerful computers continues to grow, the expectation of providing equally high performance network connectivity grows as well.
One example of a local area network, LAN 10, is depicted in FIG. 1. As shown, LAN 10 includes a server computer 14 and a plurality of client computers 16. Computers 14 and 16 are coupled by LAN hardware 12, which includes the actual transmission medium (e.g., fiber-optic cable or copper cable such as unshielded twisted pair (UTP)) as well as various network hardware elements such as hubs, switches and routers.
The advantages of LANs are numerous. By providing easy access to shared data (on server computer 14, for example), computer users are allowed to interpolate more effectively. Users are also able to share expensive peripheral devices such as printers, faxes and CD-ROMs between client computers 16. These peripheral devices are also coupled to the various client computers via LAN hardware 12. The cost of client computers may also be decreased by lessening the needs for high-capacity disk drives on individual workstations. By storing data on one or more central servers accessible through the LAN, this also provides an easier solution for backup of vital data.
A LAN includes two or more computer systems which are physically and logically connected to one another. The type of connection between the computer systems is referred to as the topology of the LAN. In a bus topology, computer systems and devices are attached at different points along a bus. Data is then transmitted throughout the network via the cable. The speed of transmission of the network is governed by the type of cable. One disadvantage of this topology is that a break in the cable disables the entire network. Furthermore, provisions have to be made for re-transmission of data in cases in which multiple computers contend for the bus (cable) at the same time, causing data collision (and possible loss of data).
Another type of topology is the ring topology, in which computer systems are daisy-chained together in a circle. In such a configuration, data is transmitted from node to node (computer to computer). The data is passed from computer to computer until the correct destination is reached. While this avoids the problem of data collision, a break in the connection disables the entire network.
A third type of topology is the star topology. In this configuration, all computer systems are routed to a central location called a hub. This allows for easy modification of the network (adding, deleting, moving computers) without having to bring down the entire network. Furthermore, the entire network does not go down if one individual connection is broken.
Hybrid topologies combining one or more of the above network configurations may also be utilized to further increase flexibility.
In order to permit a full range of data communications among disparate data equipment and networks, the International Standards Organization (ISO) developed a reference model known as Open System Interconnection (OSI) in 1974. OSI is a seven-layer model which ideally allows standardized procedures to be defined, enabling the interconnection and subsequent effective exchange of information between users. OSI defines the functions of each layer but does not provide the software and hardware to implement the model. The model""s goal is to set a standard for communication product vendors. The seven layers in sequence from top (layer 7) to bottom (layer 1) are as follows: application, presentation, session, transport, network, data link, and physical. A given network does not have to implement each layer of OSI to be compatible with this standard.
Layer 7, the application layer, is responsible for specialized network functions such as file transfer, virtual terminal, and electronic mail. The purpose of this layer is to serve as the window between correspondent application processes which are using the OSI to exchange meaningful data. Examples of application layer protocols include SNMP, RLOGIN, TFTP, FTP, MIME, NFS, and FINGER. Layer 6, the presentation layer, is responsible for data formatting, character code conversion, and data encryption of data generated in the application layer. This layer is not always implemented in a network protocol. Layer 5, the session layer, provides for negotiation and establishment of a connection with another node. To do this, the session layer provides services to (a) establish a session connection between two presentation entities and (b) support orderly data exchange interactions. This includes establishing, maintaining, and disconnecting a communication link between two stations on a network, as well as handling name-to-station address translation. (This is similar to placing a call to someone on the telephone network with knowing only his/her name, wherein the name is reduced to a phone number in order to establish the connection).
Layer 4, the transport layer, handles the reliable end-to-end delivery of data. This layer ensures that data is delivered in the same order that it was sent. It also ensures that data is transmitted or received without error, and in a timely manner. Transmission control protocol (TCP) is a common transport layer protocol. Layer 3, the network layer, routes packets of information across multiple networks, effectively controlling the forwarding of messages between stations. On the basis of certain information, this layer will allow data to flow sequentially between two stations in the most economical path both logically and physically. This layer allows units of data to be transmitted to other networks though the use of special devices known as routers. Internet Protocol (EP) is an example of a network layer protocol which is part of the TCP/IP protocol suite.
Layer 2, the data link layer, is responsible for transfer of addressable units of information, frames, and error checking. This layer synchronizes transmission and handles frame-level error control and recovery so that information can be transmitted over the physical layer. Frame formatting and cyclical redundancy checking (CRC), which checks for errors in the whole frame, are accomplished in this layer. It also provides the physical layer addressing for transmitted frame. Serial Line IP (SLIP) and Point-to-Point Protocol (PPP) are examples of data link protocols. Finally, layer 1, the physical layer, handles the transmission of binary data over a communications network. This layer includes the physical wiring (cabling), the devices that are used to connect a station""s network interface controller to the wiring, the signaling involved to transmit/receive data, and the ability to detect signaling errors on the network media. ISO 2110, IEEE 802, and IEEE 802.2 are examples of physical layer standards.
For a bus or star topology, a transmission protocol is needed for devices operating on the bus to deal with the problem of data collision (two devices transmitting data over the bus at the same time). One such technique implemented in the OSI data link layer is called carrier sense multiple access/collision detect (CSMA/CD). Under this technique, hardware residing in a network interface card (NIC) within a given computer system senses the voltage change of the bus before attempting transmission of data. If no bus activity is detected, the data is transmitted over the bus to the appropriate destination. If bus activity is detected, however, the NIC holds off the access for a predetermined amount of time before re-trying the transmission. In such a manner, the integrity of the transmitted data is preserved.
The CSMA/CD technique is employed by a LAN protocol known as Ethernet, which was developed by Xerox Corporation in cooperation with DEC and Intel in 1976. Ethernet uses a bus/ring topology and originally served as the basis for IEEE 802.3, a standard which specifies the physical and lower software layers. Ethernet technology is by far the most predominant networking protocol in use today, accounting for some 80% of all installed network connections by year-end 1996. All popular operating systems and applications are Ethernet-compatible, as are upper-layer protocol stacks such as TCP/IP (UNIX, Windows, Windows 95), IPX (Novell NetWare), NetBEUI (for LAN manager and Windows NT networks) and DECnet (for Digital Equipment Corp. computers). Other LAN technologies which are less popular than Ethernet include Token Ring, Fast Ethernet, Fiber Distributed Data Interface (FDDI), Asynchronous Transfer Mode (ATM), and LocalTalk. Ethernet is the most widely utilized because of the balance it strikes between speed, cost and ease of installation.
The Ethernet standard is defined by the Institute for Electrical and Electronic Engineers (IEEE) as IEEE Standard 802.3. This standard defines rules for configuring an Ethernet as well as specifying how elements in an Ethernet network interact with one another. By adhering to the IEEE standard, network equipment and network protocols inter-operate efficiently.
Original LANs based on Ethernet technology supported a data transfer rate of up to 10 Megabits per second (Mbps). IEEE 802.3 specifies several different types of transmission media configured to meet this transmission rate. 10Base-2 is a transmission medium which is capable of carrying information via low-cost coaxial cable over distances of up to 185 meters at 10 Mbps. This is also referred to as xe2x80x9cthin Ethernetxe2x80x9d. xe2x80x9cThick Ethernetxe2x80x9d (10Base-5), conversely, is configured to transmit up to distances of 500 m over 50-ohm coaxial cable at this same rate. A fiber-optic standard, 10Base-FL, allows up to 2,000 m of multimode duplex cable in a point-to-point link. The most popular wiring scheme at the 10 Mbps rate, however, is the 10Base-T standard, which utilizes twisted pair conductors (also called UTP-unshielded twisted pair) to carry information up to 100 m using Category 3 UTP wiring or better. UTP wiring comes in grades 1-7. Category 3 wiring supports transmission rates of up to 16 Mbps. Category 5 cable, while more expensive, can support up to 100 Mbps. Category 7 cable is the highest, most expensive grade of UTP cable.
In order to meet the demand for higher transmission speeds, the Fast Ethernet standard (IEEE 802.3 u) was established in 1995. This standard raised the Ethernet bus speeds from 10 Mbps to 100 Mbps with only minimal changes to the existing cable structure. The Fast Ethernet standard had the added advantage of being backward-compatible with the 10 Mbps Ethernet standard, allowing users to migrate to the new standard without abandoning existing hardware. Like the original Ethernet standard, Fast Ethernet includes several different transmission media. 100Base-T is a generic name for 100 Mbps twisted pair CSMA/CD proposals. Specific proposals include 100Base-T4 and 100Base-TX. The 100BASE-T4 standard allows for support of 100 Mbps Ethernet over Category 3 cable, but at the expense of adding another pair of wires (4 pair instead of the 2 pair used for 10BASE-T). For most users, this is an awkward scheme and therefore 100BASE-T4 has seen little popularity. 100Base-TX, on the other hand, is the most popular solution for a 100 Mbps Ethernet, utilizing two pairs of Category 5 UTP wiring.
Even with 100 Mbps Ethernet for LANs, new and existing network applications are evolving to embrace high-resolution graphics, video, and other rich media data types. Consequently, pressure is growing throughout the network for increased bandwidth. For example, many applications demand ultra-high bandwidth networks to communicate 3D visualizations of complex objects ranging from molecules to aircraft. Magazines, brochures, and other complex, full-color publications prepared on desktop computers are transmitted directly to digital-input printing facilities. Many medical facilities transmit complex images over LANs, enabling the sharing of expensive equipment and specialized medical expertise. Engineers are using electronic and mechanical design automation tools to work interactively in distributed development teams, sharing files which hundreds of gigabytes in sizes. Additionally, the explosion of Intranet technology is leading to a new generation of multimedia client/server applications utilizing bandwidth-intensive audio, video, and voice. In short, the accelerating growth of LAN traffic is pushing network administrators to look to higher-speed network technologies to solve the bandwidth crunch.
The Gigabit Ethernet standard proposed in IEEE 802.3z offers a migration path for Ethernet users. The IEEE 802.3z standard allows half- and full-duplex operation at speeds of 1,000 Mbps, relying on the 802.3 Ethernet frame format and CSMA/CD access method with support for one repeater per collision domain. The Gigabit Ethernet standard is also backward-compatible with 10BaseT and 100BaseT Ethernet technologies.
Much of the IEEE 802.3z standard is devoted to definitions of physical layer standards (PHYs) for Gigabit Ethernet. This standard uses the Fibre Channel-based 8b/10b coding at the serial line rate of 1.25 Gbps. Like other network models, Gigabit Ethernet implements functionality adhering to a physical layer standard. For Gigabit Ethernet communications, several physical layer standards are emerging.
Two PHYs currently exist for providing Gigabit transmission over fiber-optic cabling. A 1000Base-SX is targeted at low cost multimode fiber runs in horizontal and shorter backbone applications. 1000Base-LX, meanwhile, is targeted at multimode fiber and single-mode fiber runs in longer backbone applications, such as building backbones or campus backbones. For multimode fiber, these standards define gigabit transmission over distances of 2 to 550 meters, and for single-mode fiber, distances of 2 to 5000 meters.
There are also two standards efforts for Gigabit Ethernet transmission over copper cabling. The first copper link standard has been defined in IEEE 802.3z and is referred to as 1000Base-CX. This standard supports interconnection of equipment clusters where the physical interface is short-haul copper. It supports a switching closet or computer room as a short jumper interconnection for 25 meter distances. This standard runs over 150-ohm balanced, shielded, specialty cabling assemblies known as twinax cable. This copper physical layer standard has the advantage that it can be generated quickly and is inexpensive to implement.
The second copper link standard is intended for use in horizontal copper cabling applications. This standard is governed by the IEEE 802.03ab task force, which is chartered with the development of a 1000Base-T physical layer standard providing 1 Gbps Ethernet signal transmission over four pairs of Category 5 UTP cable, covering distances up to 100 meters or networks with a diameter of 200 meters. This standard, which uses new technology and new coding schemes in order to meet the potentially difficult and demanding parameters set by the previous Ethernet and Fast Ethernet standards, is expected to ratified sometime in late 1998 or early 1999. The 1000Base-T standard utilizes a PHY interface referred to as GMII (xe2x80x9cGigabit Medium Independent Interfacexe2x80x9d), which is similar to the MII used in 10Base-T and 100Base-X. GMII, however, provides a byte-wide interface as opposed to the nibble-wide interface of MII. MII, GMII, and TBI are discussed in greater detail below.
Regardless of the particular physical interface utilized in Ethernet, Fast Ethernet, or Gigabit Ethernet, the host CPU of the system requires access to a status register within the PHY device in order to monitor the state of the device. Device status is needed by the host CPU in order to determine if an interrupt condition is present (the link is down, for example). This status register is defined to be PHY register 1 (out of 31 possible) for both GMII and MII. (GMII also includes an Extended Status Register 15, however this only includes abilities of the device, and does not change during actual operation. This register is thus not utilized for detecting status).
The interface to the management registers of a PHY device is described in IEEE Standard 802.3u clause 22 as a two-wire interface. The standard defines a bi-directional data line (referred to as xe2x80x9cMDIOxe2x80x9d) and a clock signal (xe2x80x9cMDCxe2x80x9d). These two signal make up the management interface to the PHY device.
FIG. 2A depicts the CPU-PHY interface of a prior art computer system 100. As shown, system 100 includes a host CPU 110, a LAN controller 120, and a PHY device 130. Host CPU 110 is coupled to LAN controller 120 via a port 112. In one embodiment this port may be a system bus coupled to controller 120 via a 10 bridge chip. LAN controller is coupled to PHY device 130 by interface 122, while CPU 110 is coupled to PHY 130 via a management interface including clock signal 132 and data line 134. Computer system is coupled to an external network 140 via a transmission medium 136, such as copper or fiber cable.
For interrupt determination within computer system 100, CPU 110 needs to determine if there has been a change in a status register within PHY device 130. Given the configuration of system 100, however, CPU 110 is required to continually poll the desired register via the MDC/MDIO interface of signals 132 and 134 to detect such a change. This method creates a drain on the bandwidth of CPU 110, particularly if the polling process returns infrequent status changes. Such polling thus may affect the overall system performance.
This problem is also encountered in an alternate prior art embodiment shown in FIG. 2B. As shown, FIG. 2B depicts a computer system 150, which includes similarly numbered elements to computer system 100 of FIG. 2A. Unlike computer system 100, however, CPU 110 of computer system 150 polls PHY 130 by signaling LAN controller 120 via port 112. LAN controller 120, in turn, then polls PHY 130 via the management interface bus of signals 132 and 134. While this method avoids the direct CPU-PHY coupling of FIG. 2A, CPU 110 of FIG. 2B is still required to continually request polling information from LAN controller 130. Thus, the performance of computer system 150 is also sub-optimal.
It would therefore be desirable to have a more efficient means of polling a status register of a physical layer interface device.
The present invention comprises a network interface system and method, such as a network interface card (NIC) within a computer system, which is configured to dynamically switch between a first physical layer device and a second physical layer device in establishing a network link. The first physical layer device is coupled to a first transmission medium, while the second physical layer device is coupled to a second transmission medium. Both transmission media are operable to establish a network link. Switching may occur between the physical layer devices if an active link is determined to be down or unreliable.
The first physical layer device is one which requires a continuous connection to the computer system if active. A SERDES device is one example of such a device. If a SERDES device has established a connection with a link partner, the SERDES must be selected for active use by the NIC. In contrast, a G/MII device may establish a connection with a link partner without being selected for active use by the NIC.
The NIC includes a link switching unit coupled to both the first physical layer device and the second physical layer device, as well as a physical layer interface unit coupled to the link switching unit. The NIC further includes a control unit configured to generate a select signal indicative of whether the first physical layer device or the second physical layer device is currently selected. This select signal is then conveyed to the link switching unit and the physical layer interface unit.
The link switching unit is configured to transfer data between the physical layer interface unit and a currently selected physical layer device indicated by the select signal. The link switching unit is also coupled to the physical layer interface unit, which in turn couples to an external interface of the network interface card. The external interface connects the NIC to a remainder of the network device, e.g., a computer system.
The physical layer interface unit is configured to transfer data between the link switching unit and the external interface. The physical layer interface unit receives incoming data from both the external interface and the link switching unit. The interface unit includes a first physical layer interface sub-unit and a second physical layer interface sub-unit. The first physical layer interface sub-unit is configured to process the incoming data according to an interface of the first physical layer device, while the second physical layer interface sub-unit is configured to process the incoming data according to an interface of the second physical layer device. Both sub-units generate outgoing data in response to the incoming data. The physical layer interface unit then selects the appropriate outgoing data in response to the currently selected physical layer device.
In one embodiment, the first physical layer device is a SERDES device and the second physical layer device is a G/MII device. Accordingly, in such an embodiment, the first physical layer interface sub-unit is a physical coding sublayer and the second physical layer interface sub-unit is a G/MII reconciliation sublayer.
Dynamic switching may occur either from the first physical layer device to the second physical layer device or vice-versa. In order to switch from the first physical layer device to the second physical layer device, an indication is sent that the link established through the first physical layer device is going off-line. This ensures that link partners are notified of the pending change in link status. Next, the first physical layer device is put into isolation. The link unit is then switched from coupling to the first physical layer device to the second physical layer device. This establishes a connection from the second physical layer device to the physical layer interface unit via the link switching unit. The physical layer interface unit is then signaled that incoming data corresponds to an interface specified by the second physical layer device. Accordingly, the outgoing data generated by the second physical interface sub-unit is now selected. This establishes a connection from the link switching unit to the external interface of the NIC via the physical layer interface unit. Finally, the second physical layer device is configured and de-isolated. A network connection may now be established via the second physical layer device.
In order to switch from the second physical layer device to the first physical layer device, the process is similar. First, an indication is sent that the link established through the second physical layer device is going off-line. Next, the second physical layer device is put into isolation. Then the physical layer interface unit is signaled that incoming data corresponds to an interface specified by the first physical layer device. Accordingly, the outgoing data generated by the first physical interface sub-unit is now selected. This establishes a connection from the link switching unit to the external interface of the NIC via the physical layer interface unit. Next, the link unit is switched from coupling to the second physical layer device to the first physical layer device. This establishes a connection from the first physical layer device to the physical layer interface unit via the link switching unit. Finally, the first physical layer device is configured and de-isolated. A network connection may now be established via the first physical layer device.
This system provides a smooth migration path for network users of LANs which include both fiber-optic and copper transmission media. By having the capability to switch between a number of devices (including a fiber-optic device such as a SERDES device), network responsiveness, reliability and flexibility are enhanced. In addition, the present invention allows improved rendering of network interfaces using a single NIC. The system can be configured to monitor the active link and dynamically switch between PHYs for improved redundancy.
The present invention also comprises a system and method for monitoring a currently established network link. In prior art systems, a host CPU in a computer system is required to continually poll a register in a network interface card in order to test the status of the currently established link. This has the disadvantage of becoming a drain on the bandwidth of the host CPU, particularly if the polling does not frequently result in retrieval of updated status values. This decrease in bandwidth adversely affects system performance.
In one embodiment, the present invention includes a system for auto-polling to determine the current link status. This system includes a host CPU and a network interface card (NIC), wherein the NIC includes, a physical layer device and an auto-polling unit. The physical layer interface device is coupled to a network via a first transmission medium. Control values for this device may be changed via a management interface (such as the MDIO/MDC interface defined by IEEE standard 802.3u, clause 22). Status values for the device are included within a designated status register.
The auto-polling unit is configured to monitor activity on the management interface of the physical layer interface device. If no activity is detected on the management interface for a predetermined period of time, the auto-polling unit reads a first status value from the status register of the physical layer interface device. (The predetermined period of time may be a predefined constant, or may be varied by the host CPU). This first status value is then compared to a second status value. This second status value is the last physical layer status value read by the host CPU.
If the first and second status values are the same, the auto-polling continues monitoring activity on the management interface of the physical layer interface device. If there is a mismatch between the first and second status values, however, an interrupt is generated to the host CPU. The host CPU, in turn requests a read of the first status value (that is, the data which caused an interrupt to be generated). The read performed by the CPU causes the interrupt to be de-asserted.
Because the network interface card in this system signals the host CPU whenever an interrupt condition has been detected, the CPU does not have to waste bandwidth by continually polling network interface devices. This leads to a more efficient use of system resources, particularly CPU bandwidth. The auto-polling method used in this system thus results in increased overall system efficiency and performance.